The present invention relates to a blend of a viscosity modifier and a luminescent compound.
Luminescent polymers find use in a number of applications including roll-to-roll, screen, and ink jet printing; spin, dip, and spray coating; and “doctor blading.” While all of these applications may require materials that emit at particular wavelengths, they often widely differ in their viscosity requirements. Thus, an emitting luminescent polymer that is useful in both roll-to-roll and ink jet applications may require a high viscosity (100 cps) for the former application and a relatively low viscosity for the latter (about 10 cps).
Viscosity modification of luminescent polymers is known. For example, in U.S. Pat. No. 6,372,154, Li describes the use of low molecular weight functional additives to adjust the viscosity of luminescent inks (L-inks) that contain viscous luminescent polymers. These functional additives are described as possessing electron-transporting properties or hole-transporting properties that can be used to modify the charge transporting abilities of the L-ink in addition to viscosity modification. However, it may be desirable to modify the viscosity of luminescent polymers without changing charge transporting properties, which may adversely affect light-emitting properties. Thus, if the luminescent polymer inherently emits at a desired wavelength, it would be disadvantageous to use a modifier that reduces viscosity but concomitantly shifts the luminescent emission maximum of the blend to a wavelength substantially different from the optimal wavelength. Accordingly, it would be advantageous in the art of viscosity modification of luminescent polymers to discover modifiers that allow tuning of viscosity without substantially altering emissive properties of the neat polymer.